1. Field of the Invention
The invention relates to the process for working up hydroxide sludge residues from nonferrous metals, which essentially contain chromium, copper, zinc, and nickel as nonferrous metals, with recovery of the nonferrous metals by separating the nonferrous metals from one another.
2. Description of the Prior Art
Hydroxide sludge residues, such as are obtained from galvanic processes and in the nonferrous metal processing industry, essentially contain the following components (all data is in weight percent):
______________________________________ Water 40 to 90, average: 70 Iron 0 to 10, average: 2 Aluminum 0 to 2, average: 0.5 Chromium (III) 0 to 10, average: 2. Zinc 0 to 10, average: 2 Copper 0 to 5, average: 1 Nickel 0 to 5, average: 1 Calcium 0 to 20, average: 4 Sodium 0. to 2, average: 0.5 Silica 0 to 5, average: 1 Cyanide (complex) 0 to 0.1, - Sulfite + - Carbonate 0 to 5, - Chloride + - Sulfate + - Fluoride + - ______________________________________
These hydroxide sludge residues contain large amounts of water and such low percentages of valuable metals, that smelting of the residues cannot be carried out economically. As waste materials, however, they contaminate the environment and can be deposited only in special garbage dumps which is economically very expensive. For this reason, at least a clean removal or destruction of the waste is necessary. It is more desirable to work up the waste so as to recover the contents.
It has been proposed to eradicate such waste by admixing it with other materials and using the admixture in the manufacture of bricks. Moreover, process methods are known from hydrometallurgy and from waste water treatment which permit the recovery of one or two, but hardly more, of the components. However, the method of recovery is unsatisfactory.
There are furthermore numerous procedures for separating metals in fixed-bed ion exchangers or for removing them from effluent solutions. In this case, however, selective separation of the valuable nonferrous metals is not achieved. Generally, mixed solutions are obtained which are precipitated together, the resultant residue having to be removed as waste sludge.
A process for recovering copper and zinc from nonferrous scrap is known from German Offenlegungsschrift No. 23 40 399. According to this process, the sludge is leached with an ammonium carbonate solution in the presence of oxygen. Subsequently, the metals are separated from the copper ammonium carbonate or zinc ammonium carbonate containing leach solution. Such a process cannot be used for working up hydroxide sludge residues from nonferrous metals, since the calcium content interferes with the ammonium/ammonium carbonate equilibrium and moreover, because the chromium hydroxide would remain in the residue.
The recovery of copper and nickel by liquid-liquid extraction from ammoniacal solutions is also known as is the liquid-liquid extraction of copper at pH values of 1 to 3. These processes generally operate in conjunction with an electrolysis whose end electrolyte is used for stripping the metal-laden organic phase. There are also processes for extracting zinc with organic liquids from zinc-containing solutions of sulfuric acid. It is a common feature of all the extraction processes described that the separation can only be carried out in the absence of the accompanying elements iron, calcium, aluminum and chromium.
Attempts to precipitate nonferrous metals selectively from the waste sludge have failed because of the coprecipitation of considerable amounts of accompanying elements.